VMA Star Britney Spears Parties with Diddy, Criss Angel

Showing no pre-show jitters before her big MTV Video Music Awards performance, Britney Spears made at least two club stops filled with dancing and champagne on Friday night – first hanging with Criss Angel, then hitting a party thrown by Diddy.

At Body English in the Hard Rock Hotel, the pop star and her pals, who had a VIP table surrounded with five-dozen roses, were joined by the illusionist, with whom she's been rehearsing. "She wouldn’t stop dancing with her friends, and she looked great,” an onlooker said. After about an hour Spears left hand-in-hand with Angel.

She then popped up at PURE nightclub, where she received a warm welcome from Diddy.

"Listen up, we have Miss Britney Spears in the crowd," Diddy announced from the main stage at about 2 a.m. Saturday.

Spears had slipped into the club through a side door with six girlfriends. Wearing a strapless black mini, she held court in the VIP area, smiling, sipping champagne and dancing barefoot on a couch.

At one point, Diddy got on the microphone and told the crowd, "Britney, she holds her head up high, show some respect."

Spears ducked her head down shyly, but bounced back when her new single "Gimme More" blared over the speakers. Her friends jumped in front of her and started dancing.

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The singer left around 2:30 a.m., smiling and waving to the crowd as she walked through a path cleared by security guards and headed to Noir Bar in the Luxor.

The party appearance capped a busy day for Spears, who arrived in Vegas on Friday and rehearsed behind closed doors in the Palms Casino Resort's Pearl theater for her comeback performance to open the VMAs on Sunday night.

"I think she's focusing on performing," says music producer J.R. Rotem, who worked on seven songs for Spears's upcoming album. "I know that her passion is performing. She loves being in the studio, she loves making music, but she's a born performer. Her whole focus has been: 'I just want to get up onstage and dance.' So I'm excited because I know she is."

Rotem, who attended the BMI Urban Awards at New York New York hotel on Friday night, says the last few tumultuous years have changed Spears.

"She's in a more mature place in a way," says Rotem. "I think she's exploring topics in her music that deal with that. She still has her sexy, edgy pop stuff, but I think a person gets to a certain level of depth when they have kids so I think some of that is coming out in the music."

Producer Sean Garrett, who also worked on Spears's new album, says her new effort "is crazy" with "great material."

"Britney's really just trying to get back," he says. "She probably had time to really think about her career and is missing performing. She tried to make the right moves; she got married – she tried to do the right thing, she had kids, which everyone strives to do. It did what it did, but I think she's trying to stay grounded."